Depending on where you get your information from and how much weight you lend it, we have reached a thousand known planets.
Some of the semi-official sites like exoplanet.eu and more official sites like NASA’s Exoplanet Archive show less than this number. In the case of the latter because it appears they only accept planets that have made it past peer review, which is a reasonable, if not high, standard. In the case of exoplanet.eu, while it has been a valuable asset since 1995, it has missed a few planets here and there as time has gone on (especially during a recent overhaul of the site). There’s a number of other anomalies there, but it’s a site run by a guy in his spare time so there’s a limit to how much you can expect of it. That being said, it’s still a very valuable resource.
There exists a fairly small group of people, myself shamelessly included, who keep tabs on extrasolar planet news and developments nearly religiously. The count varies from person to person, but I am not alone in asserting that there are now 1,000 known planets. By my count, we’ve passed that a couple months ago, but I’ve decided to give it more time to help cover some margin for error in the planet count.
Where does this margin of error arise? There’s a number of planets whose disposition is not very clear. They have been proposed and later disputed, but not fully disproven. There are planets that are unconfirmed, but confident enough that they can be talked about as real planets. And lastly there are Kepler candidates that have been determined to be planets, but in some cases have not even been included in a preprint on arXiv yet. As such, it is not possible for me or anyone to point to a specific planet and say “this is the thousandth known planet.”
In the big picture, humanity’s first thousand planets is only the top layer of H2O molecules of the iceburg of the planet population in the Galaxy. It is severely plagued by biases in favour of short-period and/or high-mass planets due to the nature of our detection methods and completeness of our detection surveys. We have found many hot Jupiters, but we know full well that this is a minority (less than 1% of stars have a hot Jupiter). It’s clear that small planets are more prevalent, it’s just a matter of detecting them.
Recently, it was announced that the nearby M dwarf GJ 667C hosts three super-Earths in its habitable zone. Taken together with the two habitable planet candidates at Kepler-64 and single habitable planet candidates in other systems, we have about a dozen targets for a search for life. Some of these planets are better candidates than others, and I won’t encourage any undue optimism by refraining from being outright by saying that some of them appear pretty unlikely candidates – a few of them look like we’re scraping the bottom of the barrel in desperate hope (I’m looking at you, HD 40307 g, GJ 163 c, Kepler-22 b, GJ 581 d).
Still, the fact that our first thousand planets contains at least a few planets where it’s not impossible for life to exist there is encouraging, especially when considering how biased our detection methods are against them. Combined with Kepler data that tells us that habitable planets are ubiquitous in the Galaxy, I am actually quite optimistic about the odds for there being a second biosphere in the solar neighbourhood.
We have learned so much in the first thousand planets, detected at a slow rate at first, but growing to over a hundred per year. It has taken us 20 years to detect the first thousand exoplanets. I would not be surprised if the next thousand come in only five years and feature many more habitable planet candidates.
Lastly, I have been dealing with some events in my “personal life” that have kept me busy, and so I have had less time to focous on extrasolar planet science and writing about it here. This is partly why this post doesn’t have a lot of meat to it. I look forward to writing more enlightening posts in the near future.